Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Circular orbit of spacecraft

  1. Apr 2, 2005 #1
    An unmanned spacecraft is in a circular orbit around the moon, observing the lunar surface from an altitude of 56.0 km. To the dismay of scientists on earth, an electrical fault causes an on-board thruster to fire, decreasing the speed of the spacecraft by 16.0 m/s.

    If nothing is done to correct its orbit, with what speed (in km/h) will the spacecraft crash into the lunar surface?

    I tried finding the velocity to keep it in orbit, subtracted the decrease in speed, found the new radius and then found the new velocity it crashes with, but it is wrong. can anyone help?
  2. jcsd
  3. Apr 2, 2005 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Try using conservation of energy. What is its total energy after the slowing? What would its kinetic energy be upon impact?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook